Multi-lumen Probe

ABSTRACT

An instrument includes a probe hose in the center of which a conductor is provided for electrical supply of an electrode. Concentrically around the conductor multiple gas-guiding lumens are arranged that are isolated from one another by separation walls. The separation walls support a center section that is centrally arranged and accommodates the conductor. With this probe design particularly flexible and particularly slim probes can be created that have a particularly high dielectric strength.

RELATED APPLICATION(S)

This application claims the benefit of European Patent Application No.20202362.8, filed Oct. 16, 2020, the contents of which are incorporatedherein by reference as if fully rewritten herein.

TECHNICAL FIELD

The invention refers to an instrument for treatment of biologicaltissue, particularly for argon plasma coagulation thereof in endoscopicuse.

BACKGROUND

Endoscopic usable instruments for argon plasma coagulation are basicallyknown. WO 2008/090004 A1 discloses such an instrument having a flexiblehose and two electrodes provided therein between which a light arc canbe ignited. The hose-like instrument comprises one or two lumens,wherein in the variant having two lumens an outer probe hose and twoinner hoses are provided in which the two lumens are formed. Each lumenis assigned to one of the two electrodes. The respective electrode isconnected with a conductor that extends without own insulation over thetotal length of the instrument through the lumen that is assigned to it.The electrode is centrally held in a gas outlet opening of therespective lumen. Thereby the outer probe hose comprises an ovalcross-section.

A multiple lumen instrument is known from WO 2006/119892 A1 in which ina probe hose another hose is arranged concentrically in which anelectrode is held. For support thereof in the inner hose, it comprises ahelical-wound section with which it is supported at the inner wall ofthe inner hose. For fastening the inner hose in the center of the outerhose, radially orientated spacers are provided.

Also, a bipolar instrument is known from EP 3 205 301 Bl. Thisinstrument comprises a probe hose having a lumen and two electrodesembedded in the probe hose. While one of the electrodes is provided witha metal ring seated on a ceramic sleeve, the other electrode is locatedcentrally in the central passage of the ceramic sleeve. The ceramicsleeve forms an electrical insulator, such that an electrical barrierdischarge and thus a non-thermal plasma forms in the interior thereof.

A manual instrument provided for the open surgical use is known from EP0 353 177 A1 that comprises at its distal end an outlet channel and anelectrode arranged therein. The line provided for the supply of gas tothis manual instrument comprises multiple lumens.

Additional prior art is formed by EP 0 738 519 A1, JP 2002-301088 A andEP 3 412 234 A1.

Probes for creation of thermal plasma are subject to a remarkablethermal stress that poses limits to the design of such probes. Inaddition, high electrical voltages are necessary for plasma creationthat require a large wall thickness of the probe hose in order toachieve the necessary dielectric strength. This has to be considered forthe geometrical design of the probes and results typically to disturbingstiffness of the probe, due to the common design.

It is therefore an object of the invention to provide a basic conceptfor an instrument that achieves extended design possibilities.

SUMMARY

This object is solved with an instrument as described herein.

The instrument according to the invention can be particularly configuredas monopolar instrument that is suitable for plasma coagulation,particularly argon plasma coagulation of biological tissue. Theinstrument is particularly a flexible probe. A current flows between the(preferably single) electrode of the instrument and the biologicaltissue in the plasma forming at or flowing out of the distal end of theprobe.

The instrument (the probe) comprises a probe hose that comprises atleast two, preferably three or more lumens that can be connected to agas supply device. These lumens extend preferably through the wholeprobe hose from the proximal end to gas outlet openings located at thedistal end. Preferably no current-conducting element or an electricalconductor or an electrode is arranged in any of the lumens.

At the distal end of the probe hose an electrode is arranged preferablycentrally, the active end thereof is exposed without electricalinsulation in this area. The active end of the electrode is the sectionthereof that is in contact with the gas stream exiting the gas outletopenings and is ionizing this gas stream. Thereby the active end of theelectrode can reach remarkable temperatures of up to several 100° C. Thegas outlet openings are grouped around the electrode.

The probe hose typically comprises, due to its multiple lumenconfiguration, an outer hollow cylindrical section, a preferablyapproximately cylindrical hub or center section concentrically arrangedtherein and preferably flat separation walls arranged in between in themanner of spokes. Preferably each separation wall comprises asubstantially constant thickness from the center section to an outersection. Preferably the thickness varies about less than 20%. The centersection, the separation walls and the outer hollow cylindrical sectionare preferably parts of one and the same plastic hose that consists ofthe same material and transition seamlessly into one another. A highelectrical insulation ability and a high flexibility are obtained. Suchhoses allow extension with small radii.

The electrical insulation is originating from the conductor in radialdirection outwardly provided first and mainly by the center section. Theradius of the center section is preferably equal to or larger than theouter wall section of the hose.

Maximizing the diameter of the center section hardly influences theflexibility of the probe hose, because the center section contributeslittle to the bending stiffness of the probe. On the contrary, the outerhollow cylindrical jacket can be configured in a relatively thin-walledmanner. In doing so, fluid channels can be created in spite of the highinsulation ability provided by the center section that comprise a largefree-flowing cross-section.

The probe hose can be made of plastic that has less dielectric strengthand/or comprises a higher modulus of elasticity than material usedotherwise for argon plasma probes, such as e.g. fluoroplastics,particularly PTFE and FEP.

It is possible to provide the center section at its outer side and/orthe jacket section at its inner side with a metallization or metalinlays in order to create equipotential surfaces. Also thereby thedielectric strength of the probe hose can be further increased.

However, it is preferred to dimension the radial thickness of the centersection larger than the radial thickness of the jacket section, suchthat the electrical insulation is predominantly provided by the centersection.

The gas outlet openings are preferably concentrically arranged aroundthe electrode. The separation walls provided between the lumens of theprobe hose can be inclined relative to the radial direction. Thereby,preferably, not all of the separation walls are inclined in the samedirection. The lumens can have a cross-section substantially of atriangle with arc-shaped edges (two convex and one concave). Instead ofsharp edges, also curves can be provided. Each of the above-mentionedmeasures individually contributes that the hose has equal flexibilityand is equally insensitive against closing of a gas-guiding lumen in allradial directions due to bending the probe hose. Also the separationwalls inclined relative to the radial direction contribute to theflexibility of the probe hose and also result in that the gas uniformlyflows around the electrode.

Due to a curvature of the separation walls that is apparent in thecross-section as curvature around an axis orthogonal to thecross-sectional plane, the flexibility of the probe hose is supportedand the electrical insulation strength is particularly guaranteed alsoat bending locations of the probe hose. The separation walls are placedduring bending of the probe hose between the center section and thejacket section and increase the breakthrough field intensity. This isfor the benefit of the electrical dielectric strength.

A conductor that is, apart therefrom, not additionally insulated can beembedded in the center section of the probe hose, which is therebyelectrically insulated. Instead of a non-insulated conductor, however,also an insulated conductor can be embedded in the center section suchthat this electrical conductor is surrounded by a multi-layer insulationconsisting of different materials. Also this can be used for theimprovement of the electrical insulation or vice versa forminiaturization of the probe design. The conductor can be a wire or abraid of metal or an electrically conductive plastic. The multi-layerconfiguration of the insulation is a concept thanks to which the varietyof the usable materials for the probe hose can be increased. Forexample, the center section can consist of a material that is optimizedwith regard to its electrical insulation abilities, whereas the jacketsection (and/or also the separation walls) consist of a materialoptimized with regard to its flexibility.

The probe hose preferably comprises a constant cross-section originatingfrom the proximal end up to the gas outlet openings. The gas-guidinglumen can be arranged straight, parallel to the center axis or can alsohave a helical extension.

The jacket section may extend beyond the gas outlet openings in distaldirection such that at the distal end of the instrument a plasma chamberis formed, inside of which the distal end of the electrode ispositioned. The jacket section can consist of the material of the probehose. It is, however, also possible to make the end section surroundingthe plasma chamber of a different material, e.g. ceramic.

It is in addition possible that the electrode projects out of the probehose and is provided with a protective body at its free distal end. Theprotective body is preferably an electrically insulating body, e.g. aceramic body, e.g. a ceramic ball or any other body. Preferably thisprotective body comprises a diameter that is remarkably larger than theelectrode diameter and, for example, approximately coincides with theouter diameter of the probe hose. The protective body is preferablyrounded at its distal end surface and free of tips or sharp edges. Thisconcept is particularly suitable for radial probes that can output aplasma stream in an arbitrary radial direction. In case of an asymmetricconfiguration of the protective body, e.g. in form of an inclinedorientated ceramic disc or the like, also radial directions can bedefined for the preferred plasma output.

The electrode can be configured at its end section as bare wire end. Forexample, the wire can consist from a chromium nickel steel that has poorthermal conductivity and thus introduces low heat in the center sectionof the probe hose, where it is in direct contact with the plastic of theprobe hose. It is also possible to provide the electrode configured aswire extending through the probe hose along the total length or at leastin the section of its distal end, e.g. in the active end section, with acoating. The coating is preferably of an electrically conductivematerial. Preferably the material is a metal, the melting temperature ofwhich is less than the melting temperature of the electrode. Forexample, the coating can be made of silver or a silver alloy. Yetpreferably a further layer can be provided between the base material ofthe electrode (e.g. chromium nickel steel) and the low-melting coating,e.g. an adhesive layer, e.g. in the form of a gold layer. Suchelectrodes are steady and transfer less heat in the probe hose. Due tothe coating and the thereby achieved lower thermal stress, it is nowpossible to attach an electrode directly in the probe hose. Plateelectrodes or needle electrodes with helical base used so far, forexample, have effected an increased cooling by convection as well as acertain distancing of the discharge zone from the hose. Both can beforgone in the present invention, whereby the configuration of aflexible and miniaturized probe becomes possible.

It is in addition possible to provide an electrode extension on thedistal end of the wire extending through the probe hose. It can be, e.g.provided with a coating mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of advantageous embodiments of the invention are derivedfrom the dependent claims, the figures of the drawings as well as theassociated description. The drawings show:

FIG. 1 an inventive instrument connected to a supplying apparatus in aschematic perspective illustration,

FIG. 2 the distal end of the instrument in perspective illustration,

FIG. 3 the instrument of FIGS. 1 and 2 in a front view,

FIG. 4 the instrument according to FIG. 3 illustrating a detail in alongitudinal section,

FIG. 5 a modified embodiment of the instrument according to FIG. 4illustrating a detail in a longitudinal section,

FIG. 6 another modified embodiment of the instrument according to FIG. 4in an illustration of the distal end thereof in a longitudinal section,

FIG. 7 the distal end of another embodiment of the inventive instrumentin a partly sectional side view,

FIGS. 8 and 9 an instrument with modified probe hose in front viewrespectively.

DETAILED DESCRIPTION

FIG. 1 shows a surgical instrument 10 in the form of a multi-lumen probethat is connected to a supplying apparatus 11. The multi-lumen probe canserve for surgical treatment of a patient and can therefore beintroduced in the patient through the working channel of an endoscope.The apparatus 11 serves to supply the instrument 10 with the medium andthe electrical current necessary for operation. For example, theapparatus 11 can therefore comprise a gas source 12 and an electricalgenerator 13. The gas source 12 can be, e.g. an argon source that isformed by a gas stock provided in a pressure container, e.g. argonstock, and respective control elements, such as valves, pressureregulators and the like. The electrical generator 13 is preferably aradio frequency generator for the output of a radio frequencyalternating voltage with desired peak voltage, preferably adjustablemodulation and/or adjustable power.

The instrument 10 comprises a probe hose 14 that extends from a proximalend 15 up to a distal end 16. The probe hose 14 is a flexible hose,preferably consisting of plastic, e.g. PTFE, FEP or also PA, TPE, HDPEor PP. The probe hose 14 comprises a preferably circular-shapedcross-section on the outside, as apparent from FIG. 3. Alternatively,the cross-section on the outside can also be polygonal, e.g. hexagonalor octagonal. The cross-section on the outside is defined by acircular-shaped jacket 17 from the inside of which multiple separationwalls 18, 19, 20 extend to a hub-like center section 21 that is arrangedin the center of the probe hose, having preferably a cylindricallyshaped outer surface. Preferably an uneven number of separation walls ispresent from which a homogeneous stiffness results, i.e. a stiffnessequal in all radial directions. By means of the separation walls 18, 19,20 at least two, preferably three or more lumens 22-24 are separatedfrom one another in the probe hose 14 that respectively extend from theproximal end 15 up to the distal end 16 or up to gas outlet openings 25,26, 27 provided there and are grouped around the center section.Depending on the material and the accuracy of the extrusion, thecross-section of the outer surface and/or the cross-section of thecenter section can also be defined polygonally.

As apparent from FIG. 4, the gas outlet openings 25, 26 (and 27) aredisplaced backwardly relative to the end face of the probe hose 14 inproximal direction, such that a chamber-like depression is formed on thedistal end 16 of the probe hose 14. The active end 29 of an electrode 30extends into it, wherein the electrode 30 is held centrally in thecenter section 21. The chamber-like depression is a plasma chamber inwhich the current flow from the electrode 30 transitions on the plasmato be formed.

In the instrument 10 illustrated in FIG. 4 for emitting an axial plasmastream the active end 29 of the electrode 30 is completely arrangedinside the instrument 10 and thus in the plasma chamber. The tip of theactive end 29 of the electrode 30 is thus proximally displaced backwardrelative to the end face 28 of the probe hose 14. The electrode can alsobe located in one plane with the end face of the probe hose 14.

Originating from the electrode 30 an electrical conductor extendspreferably centrically through the center section 21 up to the proximalend 15 in order to be connected with a pole of the generator 13 there.The other pole of the generator 30 is connectible or connected with anot illustrated neutral electrode that is attachable on a patient forconducting the current back. Thus, the instrument 10 is a monopolarinstrument in which the patient is part of the treatment currentcircuit.

The electrode 30 can be configured in one single piece with theelectrical supply line 31 extending away in proximal direction and canthus be part thereof. The electrode 30 can, however, also be formed by aseparate metal element that is connected with the supply line 31.Preferably the electrode 30 consists of a material with low thermalconductivity, as e.g. stainless steel, particularly chromium nickelsteel, e.g. with the following composition:

Fe C Cr Mn P S Si Ni N Mo min 0.05 16.0 6.0 max 47.605 0.15 19.0 2.00.045 0.15 2.0 9.5 0.11 0.8

At least the active end 29 or also the whole electrode 30 can beprovided with a coating. The coating can extend also over the totallength of the conductor 31. The coating is preferably a metal coating,the melting temperature thereof being less than the melting temperatureof the electrode 30 or the active end 29 respectively. Particularly, thecoating can be formed by a silver layer. Between the silver layer andthe material of the electrode or the active end 29 of the electrode 30an adhesive layer can be provided. The adhesive layer consistspreferably of a material, the melting temperature of which is less thanthe melting temperature of the electrode 30 or the active end 29thereof. Preferably the melting temperature of the adhesive layer is,however, at least as high as the melting temperature of the coating. Theadhesive layer can be, for example, a gold layer.

In operation the electrode 30 and the conductor 31 are subject to a highvoltage that can have an amount of multiple 100 V up to multiple 1000 V.For electrical insulation of the conductor 31, the center section 21comprises a thickness in radial direction that is preferably larger thanthe thickness of the jacket 17 to be measured in radial direction. Thecenter section 21 as well as the jacket 17 contribute to the electricalinsulation of the conductor 31 relative to the surrounding endoscopeand/or the surrounding biological tissue. Due to the indicateddistribution of the material strength in favor of the center section 21,a high flexibility of the probe hose 14 is obtained. In addition, theflow cross-section of the lumens 22, 23, 24 is as large as possible. Ifrequired, the radial thickness of the center section 21 can be increasedremarkably, for example, as illustrated by a dashed circle 32 in FIG. 3.This improves the electrical insulation of the conductor 31 remarkablywithout substantially affecting the flow cross-section of the lumens 22,23, 24.

For further increase of the flexibility and/or for equalizing thebendability in all radial directions and for avoiding a lumen closureduring bending of the probe hose 14, the separation walls 18, 19, 20 canbe configured in an inclined and also curved manner, as apparent fromFIG. 3. If such a probe hose 14 is bent with a small bending radius, theseparation walls 18, 19, 20 can abut at one side of the bend against thecenter section 21, whereas the other separation walls 19, 20 can erect.Thereby always at least one, mostly two or three of the lumens are opensuch that the gas stream can flow freely in distal direction. A bendingof the probe hose 14 with a blockage of the lumens does not occur.

The instrument 10 described so far is supplied with gas, e.g. argon,during operation that flows through the lumens 22, 23, 24 parallel withone another and exits out of the gas outlet openings 25-27. It flowsaround the electrode 30 or its active end 29 that ionizes the gas streamand thus creates a plasma stream exiting distally from the instrument 10that impinges on surrounding tissue. This is connected with the counterpole of the generator 13 by means of the neutral electrode mentionedabove, such that a current flow between the active end 29 of theelectrode 30 and the tissue is established.

Due to the combination of several measures, namely

-   -   uniform gas flow from the outlet openings 25, 26, 27,    -   coating of the electrode 30, e.g. with silver, at least at the        distal end,    -   concentration of the electrical insulation in the center of the        probe cross-section, the instrument 10 can be miniaturized to        great extent. It is possible to reduce the outer diameter of the        probe hose 14 to less than 1 mm without the heat originating        from the active end 29 of the electrode 30 resulting in a quick        damaging of the probe hose 14. This applies even in the case, if        the wire or rod-shaped electrode 30, i.e. preferably configured        in a straight manner, is in two-dimensional contact at the        periphery with the plastic of the probe. A quick thermal        damaging of the probe hose is particularly avoided, if the        active end 29 is provided with a suitable coating, such as for        example, the named silver coating, that results in a        concentration of the electrical discharge to the distal end of        the active end 29 of the electrode 30. Finally a highly        miniaturizable very flexible probe is obtained that offers        fields of application for the argon plasma coagulation that have        been unreachable so far.

The structure formed particularly on the distal end 16 of the instrument10 can be produced in a manufacturing method in which a probe hoseextruded on a conductor 31 is cut first, wherein subsequently a plasmachamber 33 provided there and apparent from FIG. 4 is introduced at thedistal end 16. For this distal sections of the separation walls 18, 19,20 and, if necessary, a part of the center section 21 are removed, forexample mechanically. The electrode 30 can also be slightly shortenedsuch that it does not project beyond the end face 28 of the probe hose14. It is, however, also possible to create the plasma chamber 33, inthat the cut probe hose 14 during the first use on the patient or alsoby the manufacturer under controlled conditions is briefly operated suchthat the active section 29 of the electrode 30 as a result of the heatdevelopment melts or burns away a part of the separation walls 18, 19,20 as well as the center section 21. This process can be supported, inthat instead of argon, another suitable gas, e.g. reactive gas, such asCO₂, air or the like is used.

Numerous modifications are possible at the probe described so far. Forexample, the walls 18, 19, 20 can adjoin the center section 21tangentially as illustrated. They can adjoin there, however, alsoradially and can then transition into an inclined orientation. Also thewalls 18, 19, 20 can adjoin the jacket 17 tangentially. They can adjointhere, however, also radially and apart therefrom be in an inclinedorientation.

In all embodiments the distal end 16 of the probe hose 14 can beprovided with a sleeve-shaped element 35 that is made of a material thatis different from the material of the probe hose 14. For this FIG. 6illustrates a probe hose 14 by way of example in which the element 35 isformed by a ceramic sleeve. It can be connected to the probe hose 14 bymeans of a dull joint in a stepped joint or also on conical interface.The connection can be carried out by gluing, welding, e.g. ultrasonicwelding or by other form-fit and/or substance bond connectiontechniques. In relation to the configuration and the positioning of theelectrode 30 and its active end 29, the explanations given above applyaccordingly to the above-described embodiments.

In all embodiment described above, however, the active end 29 of theelectrode 30 can also project beyond the end face 28 of the probe hose14, as apparent from FIG. 7. In this case, the end of the electrode 30can be provided with a protective body 36, e.g. in the form of aninsulator, e.g. in the form of a ceramic element. The protective body 36is preferably rotationally symmetrically configured with regard to theactive end 29 of the electrode 30. For example, it is plate-shaped,pyramid-shaped, ball-shaped, mushroom-shaped or the like. It ispreferably configured such that with view from the electrode 30, allradial directions are free. Thus, the plasma stream can be directed in360° in any arbitrary radial direction. However, it is also possible toconfigure the protective body 36 asymmetrically and to combine it orconnect it with element 35. In this manner asymmetric operating probescan be designed.

The above description of the embodiments according to FIGS. 1-7 assumethat the conductor 31 is in direct contact with the material of theprobe hose 14. In all embodiments described above it is, however, alsopossible to provide a cable 37 instead of a bare conductor 31 thatconsists of the conductor 31 and a cable insulation 38 applied thereon.The cable insulation can be formed, for example, by an insulatingvarnish or by a plastic hose. The material of the probe hose 14 isapplied on the cable insulation 38 such that the inside of centersection 21 consists of the material of the cable insulation 38 and thematerial of the probe hose that is applied on the cable insulation 38.With this concept the safety against voltage breakthrough can be furtherincreased. The material of the cable insulation 38 can be optimized inview of maximum dielectric strength. The stiffness of the materialthereby plays a minor role. The material of the probe hose 14 can beoptimized in this case on the other hand with regard to the desiredflexibility.

For improvement of the dielectric strength at the boundary between thecable insulation 38 and the material of the probe hose 14 appliedthereon, it is possible to provide a metallization that defines acylindrically shaped equipotential surface. This can increase thedielectric strength.

It is in addition possible to orientate the separation walls 18, 19, 20radially, as illustrated in FIG. 9 and to thereby configure themstraight or also curved.

An instrument 10 according to the invention comprises a probe hose 14 inthe center of which a conductor 31 is provided for electrical supply ofan electrode 30. Concentrically around the conductor 31 multiplegas-guiding lumens 22, 23, 24 are arranged that are isolated from oneanother by means of separation walls 18, 19, 20. The separation walls18, 19, 20 support a center section 21 that is centrally arranged andaccommodates the conductor 31, wherein the center section 21 decisivelyserves for electrical insulation of the conductor 31. With this probedesign particularly flexible and particularly slim probes can be createdthat have a particularly high dielectric strength.

LIST OF REFERENCE SIGNS

-   10 instrument-   11 apparatus-   12 gas source-   13 generator-   14 probe hose-   15 proximal end of probe hose 14-   16 distal end of probe hose 14-   17 jacket-   18-20 separation walls-   21 center section-   22-24 lumen-   25-27 gas outlet openings-   28 end face of probe hose 14-   29 active end of electrode 30-   30 electrode-   31 supply line-   32 circle for illustration of an improved electrical insulation of    line 31-   33 plasma chamber-   34 sleeve-   35 element-   36 insulation body-   37 cable-   38 cable insulation-   39 radial inner beginning of face 28-   40 transition between end face 28 and outer surface

1. An instrument (10), comprising: a probe hose (14) that comprises atleast two lumens (22, 23) that are configured for being connected to agas supply device (12); an electrode (30) that is supported in the probehose (14) and comprises an active end (29); wherein each lumen (22, 23)comprises a gas outlet opening (25, 26) respectively, wherein the gasoutlet openings (25, 26) are positioned adjacent the active end (29) ofthe electrode (30).
 2. The instrument according to claim 1, wherein thegas outlet openings (25, 26) are concentrically arranged around theelectrode (30).
 3. The instrument according to claim 1, furthercomprising separation walls (18, 19) between the at least two lumens(25, 26) that extend between a center section (21) and a jacket (17) ofthe probe hose (14), wherein the electrode (30) is arranged in aninsulated manner in the center section (21) and the center section (21)has a radial thickness that is larger than a radial thickness of thejacket (17).
 4. The instrument according to claim 3, wherein theseparation walls (18, 19) are arranged in an inclined manner with regardto a radial direction of the probe hose (14).
 5. The instrumentaccording to claim 3, wherein the separation walls have a curvedconfiguration.
 6. The instrument according to claim 1, wherein the probehose (14) has a circular cross-section on an outer side thereof.
 7. Theinstrument according to claim 1, wherein the probe hose (14) is devoidof any additional electrodes and the electrode (30) is centrallyarranged in the probe hose (14).
 8. The instrument according to claim 1,wherein the electrode is embedded in an electrically insulated manner ina center section (21) of the probe hose (14).
 9. The instrumentaccording to claim 1, wherein the probe hose (14) comprises a jacketsection (17, 35) extending beyond the gas outlet openings (25, 26) in adistal direction.
 10. The instrument according to claim 9, wherein thejacket section (35) is of a different material than a material of theprobe hose (14).
 11. The instrument according to claim 1, wherein theelectrode (30) comprises a distal end that is arranged inside the probehose (14).
 12. The instrument according to claim 1, wherein theelectrode (30) comprises a distal end that is arranged outside of theprobe hose (14), wherein an insulator (36) is disposed on the distal endof the electrode (30).
 13. The instrument according to claim 1, whereinthe electrode (30) is formed by a bare end section of a wire, whereinthe wire is embedded in the probe hose (14) along an entire lengththereof apart from the bare end section.
 14. The instrument according toclaim 13, wherein the bare end section supports an electricallyconductive electrode extension (34).
 15. The instrument according toclaim 1, wherein the electrode (30) is at least in sections providedwith an electrically conductive coating.